The present invention relates to the field of underwater pipeline inspection services. More particularly, the present invention relates to a system for efficiently detecting and marking a pipeline anomaly to facilitate pipeline repair operations.
Pipeline corrosion is monitored within a pipeline to prevent accidental discharge of pressurized pipeline fluids. Pipeline inspection services are particularly important for underwater pipelines because accidental pipeline fluid releases are virtually impossible to contain after the release has occurred. Inspection services survey a pipeline to identify excessive corrosion and other potential failure points. Such services are typically performed with equipment transported through the pipeline interior.
Various techniques have been developed to perform pipeline inspection services. Self-propelled inspection devices are used in many applications and depend on complicated transport mechanisms which are subject to failure. U.S. Pat. Nos. 4,560,931 to Murakami et al. (1985) and 5,090,259 to Shushido et al. (1992) described different self-propelled systems. Certain inspection devices have transmitters for marking the device location when the inspection device becomes stuck in the pipeline. However, tapes and other recording devices within the inspection device typically monitor the pipeline anomaly location.
After a pipeline anomaly such as a structural failure or excessive corrosion is charted, divers or remotely deployed vehicles mark the pipeline anomaly. Because the divers and remote vehicles must travel to the general water surface location of the pipeline anomaly, accurate identification of the anomaly coordinates are essential to efficient repair operations. After the surface location is reached, divers or remote vehicles dive to the pipeline elevation at the locating joint identified by the inspection apparatus. The pipeline route is followed, and each buried joint is uncovered until the suspect pipeline section is reached. This process is highly inefficient and consumes valuable time. The time required for locating the precise pipeline anomaly location, and the problems of missing such location altogether, depend on the measurement accuracy monitoring the inspection equipment location when the anomaly is detected. After the pipeline anomaly is marked exterior of the pipeline, the pipelines section can be repaired with a pipeline clamp, clockspring device, or other conventional repair technique.
Different techniques have been proposed to identify the location of inspection or cleaning equipment within a pipeline. In U.S. Pat. No. 3,754,272 to Carter et al. (1973), inspection signals were recorded on magnetic tape, and the passage of the inspection apparatus at known locations as recorded and correlated against the magnetic log. U.S. Pat. No. 4,747,317 to Lara (1988) disclosed onboard inertial equipment for recording apparatus movement. In U.S. Pat. No. 4,857,851 to Anderson et al. (1989), a magnetically activated sensor detected the passage of a pipeline pig, and this information was correlated against a tape recorder carried by the pig. In U.S. Pat. No. 5,506,505 to Worthen et al. (1994), a magnetic sensor detected the passage of a pipeline pig and raised a flag in response to such passage.
U.S. Pat. No. 5,084,764 to Day (1992) disclosed another technique for inspecting a water pipeline wherein a video camera and lights were attached to a neutrally buoyant cable. The camera was pulled through a pipeline by a deployment sail as a counter monitored the length and rate of cable deployment. A drive device controlled the cable release and retrieved the cable after the surveillance operations were performed. Day described measurement inaccuracies caused by map errors and unrecorded pipeline bends, however Day did not anticipate measurement errors resulting from variations in cable tension. As the deployment sail and frictional cable drag pull a camera through the pipeline, frictional drag and binding problems between the equipment and pipeline interior wall can cause slack in portions of the cable. The inability to monitor such slack introduces errors in the cable length measurements which become significant over long distances. As previously described, such errors can significantly lengthen the time required to locate the inspection equipment location.
A need, therefore, exists for an improved system for precise identifying the location of a pipeline anomaly within an underwater pipeline, and of facilitating the marking of such pipeline anomaly. The system should be reliable, easy to deploy, inexpensive to maintain, and should identify pipeline anomaly location with a high degree of precision.